Symptoms of abnormal heart rhythms are generally referred to as cardiac arrhythmias. Various factors affect the human heart rate and contribute to changes of the heart rate from what is termed the normal sinus rate range. These rates generally range in adults from 60 to 100 beats per minute. The heart includes a number of normal pathways, which are responsible for the propagation of electrical signals from an upper chamber to a lower chamber, which are necessary for performing normal systole and diastole functions.
Treatment of arrhythmias may be accomplished by a variety of approaches, including drugs, surgery, implantable pacemakers/defibrillators, and catheter ablation. While drugs may be the treatment of choice for many patients, they only mask the symptoms and do not cure the underlying causes. Surgical and catheter-based treatments can only cure some simple cases. Implantable devices, which are widely used, will correct the arrhythmia and prevent it from occurring unexpectedly.
Cardiac pacemakers, chronically implanted within a patient's body, and connected to a heart by at least one lead, are frequently used to control bradycardiac conditions. Recently, implantable cardioverter-defibrillators, which are also implanted chronically in a patient's body and connected to the heart by at least one lead, can be used to control tachyarrhythmias and life-threatening fibrillations. There are generally two different types of body implantable leads used with cardiac pacemakers: one type, which requires surgery to expose the myocardial tissue, whereby an electrode is affixed to the epicardial tissue; the second type, which can be inserted through a body vessel, such as a vein, into the heart wherein an electrode contacts the endocardiac tissue. In the second type, the endocardial lead is often secured to the heart through the endocardial lining by a helix, hook, or tines affixed to the distal end of the lead. When the end of a lead contacts the lining of the heart at a desired location, the lead may be secured in place by utilizing lead securing means, such as screwing the helix into the heart tissue, anchoring the hook or engaging the tines.
Similarly, cardioverter defibrillators have used both epicardial leads, that is, leads with electrodes attached to the outside of the heart, and endocardial leads, that is, leads inserted into the heart through a body vessel.
With either pacing or defibrillation endocardial leads, fibrotic tissue may eventually encapsulate the leads, especially in areas where there is low velocity blood flow. When small diameter veins, through which the lead passes, become occluded with fibrotic tissue, the separation of the lead from the vein is difficult and can cause severe damage or destruction to the vein. Furthermore, separation may not be possible without constricting the movement of the lead.
In most cases, an endocardial lead will outlast its associated implanted device. However, the lead may become inoperative, or another type of lead may be required. Frequently, the existing lead is left in place, and an additional lead is implanted, rather than risking the removal of the old lead, which was now bonded to the surrounding tissue. Leaving the implanted lead in place, however, particularly in the heart, may further restrict the operation of various heart valves through which the lead passes. If several leads are left in place, operative procedures of the heart and its efficiency may be impaired. In addition, infection may occasionally develop in or around a lead, requiring surgical removal. In some cases, surgical removal may involve open-heart surgery with its accompanying complications, risks, and costs. These risks are significant for the endocardial pacemaker lead. Because the endocardial defibrillation lead is larger and more complex, the complications associated with the removal of a defibrillation lead can be even greater.
Extraction of chronically implanted leads has been difficult in the past. The problems may include lead fragility and scar tissue encountered along the vein, as well as within the heart. Intravascular countertraction techniques using locking stylets and sheaths via the implant vein, or sheaths, snares, and retrieval baskets via the femoral vein have been described in the literature. Among them, scar tissue was the primary reason for partial or failed removal of a lead. Scar tissue was usually present in multiple locations; the venous entry/subclavian area and the ventricle were the most frequent sites.
Several methods for the removal of pacemaker leads have heretofore been proposed. One method involves a lead removal tool that utilizes a hollow, rigid tube and beveled rod tip for engaging and deforming the coil structure of the heart lead. However, if such a lead can not be removed because of some complication, the tip of the tool is nevertheless locked in place and could not be removed from the lead. Consequently, both the tool and the lead would have to be surgically removed. Moreover, the rigid tube of the tool could easily puncture a blood vessel or a heart cavity wall.
Another method for transvenously extracting a lead involves manual manipulation without the use of an external tool. However, such a method is not possible if the lead has become encapsulated in a blood vessel. Moreover, this method puts excessive strain and tension on the polyurethane or silicone insulation surrounding most pacemaker leads. Should the lead break, the broken inner coil and insulation could damage the heart or surrounding blood vessels. Surgical removal of the broken lead would be imperative. Moreover, if the pacemaker lead included tines, a corkscrew, or another fixation device at the tip, pulling on the lead could seriously damage the wall of the heart.
Another technique has been disclosed in U.S. Pat. No. 4,943,289. This method generally includes the use of a stiffening stylet, which can be inserted into the lead, and then engages the inner coil of the lead near the tip, allowing tension to be applied through the stiffening stylet close to the tip of the lead. This technique also uses a pair of telescopic flexible tubes that are positioned over the lead to free fibrotic connections until the tubes are close to the distal tip of the lead. In a related U.S. Pat. No. 5,632,749, Goode et al. teaches the use of an anchoring project or expandable means associated with the apparatus for lead extraction.
Another method has been disclosed in U.S. Pat. No. 5,620,451. In this patent, Rosborough teaches the use of a flexible coil of flattened ribbon, whereby a cutting surface is provided at the distal end of the coil. It is also disclosed that the coil is radiopaque so that its use may be observed in the body by fluoroscopy or other suitable means.
What is particular interest to the present invention are radiofrequency (RF) ablation protocols, which have been proven to be highly effective in tissue ablation, while exposing a patient to minimal side effects and risks. Radiofrequency energy may be used in cutting the tissue, or separating implant parts and other substrates. Radiofrequency energy may also be utilized to trigger a memory-shaped Nitinol electrode to effect the tissue separating of the scar tissues from the implanted lead. Through a combination of the mechanical rotating cut force of the memory-shaped Nitinol electrode and the radiofrequency energy on a catheter-based device, extraction and removal of an implanted lead becomes feasible and less difficult.
There is therefore a clinical need for a device which comprises a catheter system having a sharp cutting edge of the memory-shaped Nitinol electrode with RF energy delivery capability, that is useful for extraction and removal of undesired lead by minimally invasive procedures.